1. Field of the Invention
The present invention relates to a metal coated fiber with excellent adhesion of the metal coating provided on the fiber and excellent durability under heating, as well as applications of, and a method of producing such a metal coated fiber. Specifically, the present invention relates to a metal coated fiber comprising a metal coating provided on the surface of either one, or two or more synthetic fibers such as nylon based fibers, polyester fibers, polyphenylene sulfide based fibers or polycarbonate based fibers, or natural fibers, wherein the adhesion of the metal coating is excellent, and the durability relative to external forces under heating, and the durability relative to oxygen, sulfur and chlorine and the like is also excellent, as well as applications of, and a method of producing such a metal coated fiber. Furthermore, the present invention also relates to a conductive resin composition wherein conductivity is imparted by mixing short fibers provided with a metal coating, into a substrate resin.
2. Description of the Related Art
Conductive fibers and conductive yarn formed by coating the surface of a synthetic fiber formed from a polymer material such as a nylon fiber or a polyester fiber with a thin metal film are already known. In addition, a variety of methods have been tested for improving the adhesion of the metal coating to the surface of the fiber. Examples include a method in which, in the case of a copper sulfide coating, a polymer material is pretreated using a dye containing copper ion capturing groups, and following bonding of the copper ions, the material is subjected to sulfidization (Japanese Examined Patent Application, Second Publication No. Hei 01-37513), and a method in which copper ion capturing groups are bonded to the surface of a fiber that has undergone surface roughening through treatment with alkali, and copper sulfide is then bonded to these copper ion capturing groups (Japanese Unexamined Patent Application, First Publication No. Hei 06-298973). Furthermore, in the case of materials such as aramid fiber for which metal plating is difficult, other methods such as a method in which metal ions are bonded to the surface using polyvinyl pyrrolidone (PVP), and these are then reduced to form a metal plating (Published Japanese Translation No. Hei 06-506267 of PCT) are also known.
However, the plating method using PVP described above is restricted in terms of the type of fibers, and is consequently not a general method. Furthermore, in the coating methods in which copper ion capturing groups are introduced, the metal coating is restricted to either cooper or compounds thereof, and in addition, the strength of the metal coating is not always entirely satisfactory. By treating the fiber with alkali and roughening the surface, the bonding strength of the metal coating can generally be improved, although if the degree of surface roughness and the state of the metal coating are not ideal, then a satisfactory effect may not be achievable. Moreover, in those cases in which the metal coated fiber is used for clothing and the like, the fiber must be capable of withstanding severe usage conditions including washing and abrasion In addition, from the viewpoint of conductivity, even a partial separation of the metal coating invites a disconnection, and consequently the metal coating requires an adhesive strength with a high level of reliability.
In addition, recently conductive resin compositions are being produced by mixing conductive fillers into a resin which acts as a substrate. Examples of the materials used as these conductive fillers include powders and fibers formed from conductive compounds such as conductive metals or alloys thereof, or metal oxides. However, in materials utilizing conductive powders or metal particles, relatively large quantities must be used to ensure that these powders or particles mutually contact within the resin, and consequently the weight of the resin composition increases. Moreover, the contact surface area of powders or particulate matter is not particularly large, and consequently even if large quantities are used, achieving a high level of conductivity is difficult. In contrast, metal fibers mutually intertwine, maintaining a state of good contact, and consequently the quantities used can be less than in the case of metal powders, although the metal fibers themselves are heavier than the resin, and consequently the weight of a resin composition containing such metal fibers increases. Furthermore, metal fibers do not possess the flexibility of resin fibers and consequently if the quantity of metal fiber is increased, then the flexibility and durability of the resin composition suffers. A different technique involves the use of metal whiskers (needle like crystals), although there is a possibility that fine metal fibers, metal whiskers, or needle like metal oxides and the like can be sucked into the respiratory organs and cause damage, and as such they are almost never used these days.
Furthermore, resin fibers with metal coatings do not display satisfactory coating strength, and if subjected to mix spinning with a typical single fiber, then problems can arise such as separation of the metal coating during processing, or separation of the metal coating some time after completion of the mix spinning, resulting in a reduction in conductivity, and consequently such fibers offer only limited practicality. In addition, the production costs associated with long fibers with a uniform metal coating are high.
The present invention aims to resolve these types of problems associated with conventional metal coated fibers and conductive resin compositions, and has an object of providing a metal coated fiber with excellent coating strength and corrosion resistance. Furthermore, another object of the present invention is to provide a conductive resin composition with excellent conductivity, wherein the conductivity can be maintained with good stability over an extended period.